DeskTape will use this compression setting when initializing the next tape.

If the tape is not mounted, use the HDC check box in the DeskTape control panel to control compression.

Not all tape drives report/support both tape sizes. Use the smaller tape with these drives. 

Enters the maximum volume size allowed for this compression setting.

The smallest volume size is 40 MB. The largest volume size depends if you have compression. Also, the Mac file system limits you to 2048 MB.

Tapes always mount with the size and compression state they were initialized under.

Your drive does not support DDS-DC hardware data compression.